The Vaccine Symposium will focus on basic aspects of antigen presentation, with a special attention to the role of MHC class II and the generation of antibodies. Over the last few years, MHC class l-restricted cytotoxicity lymphocytes (CTL) have been in the limelight. However, vaccine strategies aimed at generating CTL responses have only been partially protective and have not provided protection from infection. In contract, passive immunization studies by various groups have clearly shown that neutralizing antibodies can provide complete protection from infection. A challenge to scientists in the AIDS vaccine development field is now to find ways of generating neutralizing antibodies with the desired epitope specificities at sufficiently high levels through active vaccination using novel immunogens. Lastly the topic of innate immunity and its role in leading to adaptive immune responses will also be highlighted. The HIV vaccine meeting program has been put together to provide the scientists with the most recent information on how immune cells fight off foreign invaders. The focus of the meeting is on discussing new approaches to generate antibodies which are soluble protein molecules, against the AIDS virus. Because the virus keeps changing its env molecules rapidly, finding antibodies that recognize most, if not all,forms of the HIV env has been difficult. New insights into the structure of the AIDS virus env molecules will be discusses, along with new approaches to develop vaccines that can induce antibodies against multiple strains of the AIDS virus. The Keystone Symposium on HIV Vaccines ranks as the premier venue for the latest research aimed at HIV vaccine research.